6.4.19 Floor decking
Floor decking shall be suitable for the intended use and be of adequate strength and moisture resistance. Issues to be taken into account include:
- type, thickness and fixing
- protection against damage.
Type, thickness and fixing#
Where decking contributes to the sound insulation of a floor, the thicknesses listed in this chapter should be checked.
Floor decking should:
- be appropriate to the joist spacing
- be in accordance with Table 7 (which applies to normal domestic loads, ie, an imposed load of 1.5kN/m2), or comply with another acceptable clause described in Technical Requirement R3.
Table 7: Floor decking requirements
| Floor decking | 400mm joist centres | 450mm joist centres | 600mm joist centres | Standard |
|---|---|---|---|---|
| Softwood boarding | 16 | 16 | 19 | BS EN 13353 |
| Moisture resistant chipboard | 18 | 18 | 22 | BS EN 312 – type P5 |
| Plywood | 15 | 15 | 18/19 | BS EN 636 |
| Oriented strand board | 15 | 15 | 18/19 | BS EN 300 – type OSB3 |
When installing decking:
- fixings and support should be in accordance with the manufacturer’s recommendations
- checks should be made, prior to fixing, to ensure that noggings, blocking and strutting are in the correct position and secure
- butt joints should be staggered and supported on noggings or joists
- adjacent boards should be square
- where nails are used, they should be 2.5 x the thickness of the decking material
- where gluing is required, boards should be glued to the joists and at joints, using a suitable polyvinyl acetate (PVAc) adhesive
- temporary wedges and packing should be removed once the floor decking is complete.
Square edged boards and boards with loose tongues
When fixing boards with square edges or loose tongues, they should be supported on all sides by joists or noggings.
Tongued and grooved boards
When fixing boards with tongued and grooved edges:
- boards should be laid with long edges at right angles to joists
- short edges should be supported on joists or noggings or cut back to form a butt joint over a joist
- boards should be glued to the joists and the sheets glued to each other with polyvinyl acetate (PVAc) adhesive (not softwood boarding)
- long edges at room perimeters should be fully supported on joists or noggings.
Chipboard flooring
Chipboard flooring should be supported and fixed in accordance with manufacturers’ recommendations using either:
- flat-headed ring shank nails, 2.5 x the thickness of the board and minimum 3mm diameter, or
- screws to BS 1210, minimum 2 x the thickness of the board and no less than size No. 8.
When fixing:
- fixings should have a maximum spacing of 300mm along continuously supported edges and intermediate supports
- where boards abut a rigid upstand, a minimum 10mm expansion gap should be provided; for large areas of boarded floor, a wider expansion gap may be required at upstands and intermediate expansion gaps of 2mm per linear metre of floor should be provided.
Oriented strand board flooring
When fixing oriented strand board flooring:
- boards should be laid over supports in the direction indicated on the board, with the stronger axis at right angles to the supporting joists
- boards should be long enough to span two joists
- nails should be flat headed, annular grooved nails, 3mm in diameter
- where boards abut a rigid upstand, a minimum 10mm expansion gap should be provided; for large areas of boarded floor, a wider expansion gap may be required at upstands and intermediate expansion gaps of 2mm per linear metre of floor should be provided.
Plywood flooring
When fixing plywood flooring:
- boards should be laid with the face grain at right angles to the supports
- end joints should occur over joists or noggings
- fixings should have a maximum spacing of 150mm around the perimeter and a maximum spacing of 300mm on intermediate supports
- an expansion gap of at least 1.5mm-2mm should be allowed between each panel.
Nails for fixing plywood should be in accordance with Table 8.
Table 8: Fixings for plywood floors
| Plain wire nails (mm) | Annular ring shank nails (mm) | |
|---|---|---|
| Minimum diameter | 3.35 | 3 |
| Minimum length | 65 | 50 |
| Minimum penetration | 40 | 32 |
Proprietary flooring
Proprietary flooring should be:
- certified in accordance with Technical Requirement R3
- installed in accordance with certification requirements.
Protection against damage#
Floor decking should be stored:
- on a hard base
- under cover
- indoors where possible.
Floor decking that are built in as the work proceeds and left exposed to the weather will be subjected to deterioration and adverse effect of the weather, particularly when exposed to prolonged periods of rainfall. Such floor decking when used in conjunction with engineered and traditional joists should:
- have a third-party approval certificate from a UKAS accredited body which covers weather resistance for the period of time the boards are to be left exposed on site
- be used strictly in accordance with the manufacturer’s instruction and details.
Any floor decking that are left exposed beyond the period stated on the third-party approval certificate should be replaced.
Non-proprietary floor decking without third party certification should not be used on structural floors exposed to the weather for any period of time under any circumstances.
Floors should not be overloaded, especially with materials during construction, and be protected against damp, plaster splashes and other damage.
Last updated: 2nd January 2024